Dual-loop control for laser annealing of semiconductor wafers

Patent metadata

Field	Value
Publication number	US-9475150-B2
Application number	US-201414185072-A
Country	US
Kind code	B2
Filing date	Feb 20, 2014
Priority date	Dec 6, 2012
Publication date	Oct 25, 2016
Grant date	Oct 25, 2016

Abstract

Systems and methods for performing semiconductor laser annealing using dual loop control are disclosed. The first control loop operates at a first frequency and controls the output of the laser and controls the 1/f laser noise. The second control loop also controls the amount of output power in the laser and operates at second frequency lower than the first frequency. The second control loop measures the thermal emission of the wafer over an area the size of one or more die so that within-die emissivity variations are average out when determining the measured annealing temperature. The measured annealing temperature and an annealing temperature set point are used to generate the control signal for the second control loop.

First claim

What is claimed is:

1. A laser annealing system for annealing dies supported by a wafer having melt temperature and a surface that supports dies each having a variation in emissivity, comprising:
a chuck that supports the wafer, and a movable stage that supports the chuck and that is adapted to move the chuck and wafer;
a laser that generates an initial laser beam and that has an adjustable output power and an amount of 1/f noise that can cause variations in an annealing temperature, wherein the annealing temperature is less than the wafer melt temperature;
an optical system configured to receive the initial laser beam and form therefrom an annealing laser beam and to direct a portion of the annealing laser beam to a photodetector system that in response generates a detector signal, the optical system being arranged so that the annealing laser beam is made incident upon and scans over the wafer surface due to the movement of the wafer, and heats the wafer to the annealing temperature;
a thermal emission detector system arranged relative to the wafer surface and configured to receive thermal emission radiation therefrom that is generated by the annealing laser beam and average the received thermal emission radiation over an area of one or more of the dies, and in response generates a thermal emission signal;
a first control loop configured to receive the detector signal and control the laser to adjust the output power at a first frequency f 1 in the range from 1 kHz to 100 kHz to reduce the amount of 1/f noise; and
a second control loop configured to receive the thermal emission signal and control the laser to adjust the output power at a second frequency f 2 in the range from 1 Hz to 100 Hz to reduce variations in the annealing temperature.

2. The system of claim 1 , wherein the annealing temperature is in the range from 400° C. to 1350° C.

3. The system of claim 1 , wherein the thermal emission signal includes spikes, wherein the thermal emission detector system includes a filter, and wherein the thermal emission signal is passed through the filter to reduce or eliminate the spikes.

4. The system of claim 1 , wherein the first and second control loops respectively include first and second proportional-integral-derivative controllers that are coupled to one another.

5. A dual-loop control system for a laser annealing system that uses an annealing laser beam from a laser having 1/f noise and a controllable output power to anneal a wafer having a melt temperature and dies that each have a variation in emissivity, comprising:
a first control loop operating at first frequency f 1 in a range between 1 kHz and 100 kHz and configured to control the laser output power to reduce the 1/f laser noise that can cause variations in an annealing temperature, wherein the annealing temperature is less than the wafer melt temperature; and
a second control loop operating at a second frequency f 2 in a range between 1 Hz and 100 Hz and that measures thermal emission radiation from the wafer over an area of one die or greater, the thermal emission being caused by the annealing laser beam heating the wafer to the annealing temperature, the second control loop being configured to determine a measured wafer temperature from the measured thermal emission radiation and generate a measured temperature signal, which is used in combination with an annealing temperature set point signal to control the laser output to reduce variations in the annealing temperature.

6. The dual-loop control system of claim 5 , wherein the second control loop includes a thermal emission detector system that measures the thermal emission within one or more dies and then averages the within-die measurements to said area of one die or greater.

7. The dual-loop control system of claim 5 , wherein the first control loop includes a photodetector system that receives a portion of the annealing beam created by a beam-turning element, the photodetector system generating in response a detector signal representative of an amount power in the annealing laser beam, and wherein the first control loop includes a first proportional-integral-derivative (PID) controller that receives the detector signal as well as a second control signal from the second control loop and that generates a first control signal in response thereto and sends the first control signal to the laser.

8. The dual-loop control system of claim 7 , wherein the second control loop includes a second PID controller that receives the measured wafer temperature signal and the annealing temperature set-point and in response generates the second control signal.

9. The dual-loop control system of claim 5 , wherein the second control loop includes emission to temperature (E/T) logic that calculates the measured temperature from the measured emission.

10. The dual-loop control system of claim 9 , wherein the second control loop includes a low-pass filter that filters the measured temperature signal from the E/T logic prior to inputting the measured temperature signal to the second PID controller.

11. A laser annealing system for performing laser annealing of a wafer having a melt temperature and a surface that supports an array of dies with each die having a varying emissivity, comprising:
means for scanning an annealing laser beam from a laser over the array of dies, wherein the laser has an amount of laser noise and is adjustable to control an amount of power in the annealing laser beam, wherein the annealing laser beam creates an annealing temperature at the wafer surface that does not exceed the wafer melt temperature;
means for measuring and controlling the amount of power in the annealing laser beam using a first control loop that measures the amount of power and operates at a first frequency f 1 to control the amount of laser noise in the laser; and
means for controlling the amount of power in the annealing laser beam using a second control loop that operates at a second frequency f 2 <f 1 by measuring thermal emission radiation from the wafer, including averaging the thermal emission radiation over at least one die and determining therefrom a corresponding average measured temperature, and using the average measured temperature and an annealing temperature set point to adjust the laser to control the amount of power in the annealing laser beam.

12. The system of claim 11 , wherein the first frequency f 1 is in a range from 1 kHz to 100 kHz and the second frequency f 2 is in the range from 1 Hz to 100 Hz.

13. The system of claim 11 , wherein f 1 is about (100)·f 2 .

14. The system of claim 11 , wherein measuring the amount of power in the laser annealing beam includes deflecting a portion of the laser annealing beam to a photodetector system.

15. The system of claim 14 , wherein deflecting a portion of the laser annealing beam includes diffracting a portion of the laser annealing beam using a grating formed on a reflective surface from which the laser annealing beam otherwise reflects.

16. The system of claim 11 , wherein the system is configured such that the step of measuring the thermal emission radiation from the wafer is performed at Brewster's angle.

17. The system of claim 11 , wherein the first and second control loops respectively employ first and second proportional-integral-derivative controllers that are coupled to one another.

18. The system of claim 11 , wherein the laser annealing beam creates an annealing temperature at the wafer surface in the range from 400° C. to 1350° C.

Assignees

• Mcwhirter James T
• Gaines David
• Lee Joseph
• Zambon Paulo
• Ultratech Inc

Inventors

• Mcwhirter James T
• Gaines David
• Lee Joseph
• Zambon Paulo

Classifications

• B65D5/0281

  the tubular body presenting double or multiple walls (for thermal insulating purposes B65D81/3853) · CPC title

• B65D81/03

  Wrappers or envelopes with shock-absorbing properties, e.g. bubble films {(for thermal insulating purposes B65D81/3888)} · CPC title

• B65D5/029

  the tubular body presenting a special shape (pyramidal B65D5/008) · CPC title

• B23K26/0066 Primary

  Operations & Transport · mapped topic

• B65D5/02 Primary

  by folding or erecting a single blank to form a tubular body with or without subsequent folding operations, or the addition of separate elements, to close the ends of the body (specially constructed to allow collapsing and re-erecting without disengagement of side or bottom connections B65D5/36) · CPC title